This invention relates to controlled administration of chemodenervating agents, e.g., botulinum toxin-derived pharmaceuticals, useful in attenuating neural stimulation and spasmotic activity of muscle. More particularly, the invention relates to a method of standardizing denervating pharmaceuticals and novel dosage forms based thereon which permit medically safe administration in the management of a variety of diseased states and injuries characterized by involuntary muscle spasm or hyperactivation. The invention also relates to novel methods of administering chemodenervating agents in a controlled and reproducible manner so as to confine their effect to a given region of muscle mass while minimizing paresis in adjacent muscle tissue.
Pharmaceutical grade preparations from the toxin produced by Clostridium botulinum have been available for many years from Dr. Allan Scott and the Kettlewell Ophthamology Institute of San Francisco, Calif., and now is sold commercially by Allergan Pharmaceuticals, Inc. Many other materials toxic to neuromuscular transmission are known, such as tetanus toxin and various subtypes of botulinum toxin. Botulinum toxin preparations recently have been approved for the treatment of blepharospasm and strabismus, and clinical trials are underway on the treatment of spasmodic torticollis. Dykstra et al have proposed in U.S. Pat. No. 4,932,936 that botulinum toxin can be used in the treatment of spasmodic sphincter muscle which leads to urinary incontinence ("neurogenic bladder") characteristic of some forms of cancer. A survey of the literature provides evidence for the potential use of chemodenervating agents such as botulinum toxin in the treatment of other significant spasmodic diseases including jaw dystonias, occupational dystonias, corneal ulceration (protective ptosis), spasmodic dysphonia, and various forms of facial dyskinesis including Meige syndrome, hemifacial spasm, aberrant regeneration of facial nerves, and apraxia of eyelid opening.
Treatment of these diseases involves injection of a chemodenervating agent, currently a botulinum preparation, directly into the muscle, using, for example, a fine gage teflon-coated needle under electromyographic control to aid the physician in locating the intended intramuscular locus of the injection. The pure active toxin is believed to be the single most toxic material known. A sufficient dose of the toxin acts on striated muscle to block release of the acetylcholine neurotransmitter from the presynaptic membrane resulting in varying degrees of effective denervation of the muscle in regions contacted by the toxin. This results in an increase in post-synaptic acetylcholinesterase activity and an increase in the population of acetylcholiee receptors, effects which occur as a characteristic physiological response to denervation. After a period of days, the axon terminals develop sprouting, and over a period of several months, collateral motor axons establish new neuromuscular connections with the muscle fiber. As neuromuscular junctions are regenerated, full function of the muscle returns along with the spasmodic contractions or hyperstimulation symptomatic of the disease.
With the exception of the emerging spasmodic torticollis therapy, development of the therapeutic uses of botulinum toxin preparations has been limited to small muscles which may be treated with lower doses and have limited risk of toxin spread. Development of the therapies has proceeded empirically using low doses without theoretical basis or clinical data predictive of the distribution of the toxin in vivo. Currently, toxin preparations are quantified by measuring the LD.sub.50 in white mice. LD.sub.50 in white mouse equals one international unit or I.U.
The treatment of blepharospasm with botulinum toxin as disclosed by Borodic et al in Plastic and Reconstructive Surgery. (March, 1989) is illustrative of a protocol for use of the toxin. Generally, for bilateral blepharospasm, a starting dose totalling 10 to 20 IU is injected at 4 to 6 sites in the upper and lower eyelid of each eye spaced laterally from the midline of the lid and close to the lash base of the upper lid. Injections above the brow are given only if significant involuntary movements are recurring in this region. If the toxin is injected too close to the upper lid fold, diffusion through the orbital septum can weaken the levator palpebrial superioris muscle and induce ptosis. If the toxin is injected too medially in the lower lid, the naso-lacrimal pumping mechanism can be weakened excessively resulting in epiphora. With an appropriate dose, because the muscle is only partially weakened, enough strength and neural control remain so that a treated muscle still can perform its primary voluntary function. The degree of weakening from denervation can be "titrated" empirically for particular patients by altering the dose.